In order to reduce spoofing and provide a safer client experience, Office 365 now supports inbound validation of DomainKeys Identified Mail (DKIM) over IPv4, and Domain-based Messaging and Reporting Compliance (DMARC). Both of these technologies check for trusted authenticated senders and help identify untrusted ones that that fail authentication. Exchange Online Protection (EOP), which filters every single mailbox on Office 365, had previously supported Inbound DKIM for IPV6. With these added functionalities feature, Office 365 users can expect better brand protection and an even safer experience.
Continue reading at source: http://blogs.office.com/2015/01/20/enhanced-email-protection-dkim-dmarc-office-365/